Cincinnati Zoo Under 24-Hour Baby Watch as it Waits for Fiona the Hippo's New Sibling to Arrive

Cincinnati Zoo/Facebook

Fiona the hippo is about to become a big sister!

After announcing Bibi the hippo's pregnancy with dad-to-be Tucker in April, the Cincinnati Zoo is now under a 24-hour birth watch for Fiona's younger sibling, according to WLWT5.

Bibi is due in mid-August, but the hippo's birth window could be 30 days before or after the estimated due date, so the zoo is ready for Fiona's sibling to arrive at any moment.

In July, the Ohio zoo shared an update on Instagram about the upcoming hippo baby.

"According to measurements made during Bibi's last ultrasound, her fetus is bigger than Fiona was when she was born!" the Cincinnati zoo shared. Bibi's first baby, Fiona, was born six weeks premature and wouldn't have survived without the intervention of zookeepers. Fiona's resiliency and continued success have made her a star at the Cincinnati Zoo.

"The hippo team is optimistic that the baby will be born within the normal birth window," the zoo added on Instagram.

When Fiona was born in 2017, she only weighed 29 pounds, 25 pounds less than the lowest ever record weight for her species. Ahead of her sibling's arrival, Fiona celebrated one of her own accomplishments.

"Fiona finally hit 2,000 pounds! She weighed in at 2,036 pounds this morning!" the zoo shared on Instagram in July. "We're so proud of how far she has come! 🦛🎉🎉🎉 #TeamFiona"

The Ohio zoo officially announced Bibi's pregnancy in a release in April.

"The hippo team is excited and also nervous," Eric Byrd, the manager of Cincinnati Zoo's Africa team, said in a statement about the pregnancy.

Reproductive physiologists at the zoo's Center for Conservation and Research of Endangered Wildlife (CREW) are working with Bibi's caretakers to ensure the mother hippo gets everything she needs during the pregnancy.

RELATED: Baby Girl Named After Fiona the Hippo Meets the Cincinnati Zoo Animal for the First Time

Cincinnati Zoo & Botanical Garden

RELATED: Cincinnati Zoo's Fiona the Hippo is 'Best Buds' with New Male Hippo Tucker

The dad of Bibi's new baby is 18-year-old Tucker, who arrived at the zoo in September 2021, several years after the death of Fiona's father, Henry. Tucker made the move to Ohio as part of a breeding recommendation from the Association of Zoos and Aquariums (AZA) Species Survival Plan (SSP) Program — the group responsible for managing the health and genetic diversity of the hippo population in North American zoos — but the zoo wasn't planning for Bibi and Tucker to become parents just yet.

"We weren't planning to welcome a baby this soon, but nature found a way and ignored our calendar," Christina Gorsuch, the Cincinnati Zoo's director of animal care, shared in the zoo's pregnancy announcement. "Most forms of contraception, in hippos or humans, are not 100% reliable. The dose that was previously effective for Bibi did not prevent pregnancy this time."

RELATED: Fiona the Hippo Catches Raindrops in Her Mouth at the Cincinnati Zoo

The Cincinnati Zoo teased that a new hippo was on the way on National Siblings Day, April 10, when it posted a photo of Bibi's ultrasound on Facebook.

The zoo followed up this clue with another Facebook post featuring a shot of three large watermelons and one small watermelon.

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"We're gonna need more watermelon!" read the post, which the zoo shared several hours before breaking the baby news.

Fans of Fiona and her family can keep updated on Bibi's pregnancy on the zoo's social media accounts, according to the Cincinnati Zoo.